Aristotle · a new plain-English translation from the original language
1| So it is possible for the female mule sometimes to conceive, as has evidently already happened, but to nourish the young and carry it to term is impossible. The male might at some point sire offspring, both because the male is by nature hotter than the female, and because the male contributes no bodily matter to the mixture in generation. What is thus produced becomes a ginnos. This is a stunted mule; for ginnoi are also produced directly from the horse and the donkey, when the embryo suffers some defect in the womb. For the ginnos is like the metachoira among pigs; for there too, the offspring stunted in the womb is called a metachoiron. Any of the piglets, whichever it happens to be, may turn out this way. Pygmies come about in the same way; for they too have their parts and their size stunted during gestation, and are like the metachoira and the ginnoi.
2| We have discussed, then, the childlessness of mules, and the animals that bear live young, both those that do so outwardly and those that do so within themselves. Among the blooded animals that lay eggs, in one respect the facts about their generation are similar both to each other and to the land animals, and one can grasp something the same about all of them, but in another respect they differ, both from each other and from the land animals. Now all of them come to be from copulation without exception, the male emitting seed into the female. Among the egg-layers, the birds emit a complete, hard-shelled egg, unless something is defective through disease, and all the eggs of birds are two-colored. Among fish, the cartilaginous ones, as has often been said, lay eggs within themselves and then bear live young, the egg shifting from one place in the womb to another; their egg is soft-shelled and uniform in color. Only one of these does not bear live young within itself, the so-called fishing-frog; the cause of this must be stated later. The rest of the egg-laying fish emit an egg that is uniform in color but incomplete, for it takes its growth outside, for the same reason that also applies to the eggs that are completed inside.
3| We have already discussed, then, what differences the wombs have and for what causes. For among the live-bearers, some have their womb up near the diaphragm, others down near the joints — up in the cartilaginous fish, down in those that bear live young both within themselves and outwardly, such as man and horse and each of the other such animals. And among the egg-layers, some have it down, as do the egg-laying fish, others up, as do birds. Now conceptions also form in birds spontaneously — what some call wind-eggs and zephyr-eggs; these occur in birds that are neither strong fliers nor hook-taloned, but are prolific, because such birds have much residue, whereas in the hook-taloned birds this kind of secretion is diverted into the wings and feathers, and their body is small, dry, and hot, while the menstrual secretion and the seed are residue. Since, then, both the nature of feathers and that of seed come from residue, nature cannot pour abundantly toward both at once. For this same cause the hook-taloned birds are neither given to mating nor prolific, while the heavy birds, and among fliers all those whose bodies are bulky, such as the pigeon and the like, are given to mating and prolific.
4| For in the heavy, non-flying birds, such as hens, partridges, and others like them, much residue of this kind arises; hence their males are given to mating and their females emit much matter, and such birds produce their young either many at a time or often — many at a time, as the hen, the partridge, and the Libyan ostrich; the pigeon kind not many at a time, but often, for these stand between the hook-taloned and the heavy birds. They are fliers, like the hook-taloned, but they have bulk of body, like the heavy ones, so that because they are fliers, and their residue is diverted there too, they lay few eggs at a time, but because of the bulk of their body, and because they have a hot and highly digestive gut, and besides this because they procure their food easily, while the hook-taloned do so with difficulty, they lay often. The small birds too are given to mating and prolific, as sometimes plants are as well; for growth into the body becomes seminal residue. This is why, among hens, the Adriatic breed is the most prolific of all: because of the smallness of their body, the nourishment is spent on breeding.
5| Also the ignoble breeds are more prolific than the noble ones; for the bodies of the former are moister and bulkier, those of the latter leaner and drier, since noble spirit arises more in bodies of that leaner sort. Further, the thinness and weakness of the legs also contributes to such birds' being disposed to mate and being prolific, as is also the case with humans; for in them the nourishment that would go to the limbs is diverted into seminal residue — what nature takes away from there, it adds here. The hook-taloned birds have a strong stance and legs with bulk, because of their way of life, so that for all these causes they are neither given to mating nor prolific. The kestrel is the most prolific of all; for it is almost the only one of the hook-taloned birds that also drinks, and its moisture, both natural and acquired, is seminal, together with the heat that belongs to it. Yet even it does not produce very many at a time, but four at most. The cuckoo produces few young, even though it is not hook-taloned, because it is cold by nature (its cowardice makes this clear), whereas a seminal animal must be hot and moist. That it is cowardly is plain:
6| for it is chased by all the birds, and it lays its eggs in the nests of others. The pigeon kind, on the other hand, usually lays two eggs; for they are neither one-egg layers (no bird lays only one, except the cuckoo, and even this one sometimes lays two), nor do they lay many, but often produce two or three at most, and mostly two; for these numbers stand between one and many. That in prolific animals the nourishment is diverted into seed is clear from what happens. Most trees, after bearing too much fruit, wither away afterward, when no nourishment is left over for the body, and annual plants appear to suffer the same thing — such as pulses, wheat, and the like; for they spend all their nourishment on seed, since their kind produces much seed. And some hens that have been excessively prolific, to the point of laying two eggs in a day, have died after this excessive laying. For birds and plants too become depleted; and this affliction is an excess in the discharge of residue. A condition of this kind is also the cause of the lion's later barrenness: for at first it bears five or six cubs, then in the following year four, then again three cubs, then the next number down to one, then none at all, as the residue is used up and, at the same time as its age comes to an end, the seed fails.
7| We have now said, then, in which birds wind-eggs occur, and further which of them are prolific and which produce few young, and for what causes. Wind-eggs occur, as has also been said before, because the seminal matter is present in the female, but birds do not produce the menstrual discharge as the blooded live-bearers do; for in all of these it occurs, more in some, less in others, and in some in such quantity as at least to be noticeable. It is likewise the case, though not identically, with fish as with birds; hence in them too a conception forms without mating, just as in birds, but less conspicuously, since their nature is colder. The discharge of menstrual matter that occurs in live-bearers takes shape, in birds, according to the times when the residue arrives, and because the place near the diaphragm is hot, it is brought to completion there in its full size. But with respect to generation, these too, and likewise the eggs of fish, are incomplete without the seed of the male; the cause of this has been stated before. Wind-eggs do not occur in the strong-flying birds, for the same reason that such birds are also not prolific.
8| For hook-taloned birds have little residue, and need the male in addition for the impulse of the discharge of the semen. Wind-eggs are more numerous than those produced by mating, but smaller in size, for one and the same cause: they are smaller in size because they are incomplete, and because their size is smaller they are more numerous in number. They are also less pleasant to the taste because they are less concocted; for in all things what is concocted is sweeter. That the eggs neither of birds nor of fish are brought to completion for generation without the males has now been sufficiently observed. But as to whether conceptions also occur in fish without males, the case is not the same throughout; in connection with the erythrinus, for some are seen to have eggs immediately, as has been written about them in the Researches. And in general, even among birds, the eggs produced through mating tend for the most part not to grow unless the bird is covered continuously. The cause of this is that, just as in women intercourse with males draws down the discharge of the menses (for the womb, being heated, draws the fluid, and the passages open up), the same thing happens also in birds as the menstrual-type residue advances little by little; this residue is not discharged outward, because it is small in quantity and because the wombs lie up near the diaphragm, but it drains together into the womb itself.
9| For this is what makes the egg grow, just as with the embryos of live-bearing animals through the umbilical cord — what flows in through the womb — since once birds have mated once, nearly all of them go on continually having eggs, though quite small ones. This is why some are accustomed to say of wind-eggs that they are not generated at all but are remainders left over from an earlier mating. But this is false; for it has been sufficiently observed occurring even in the chicks of the hen and the goose without any mating. Further, female partridges — both those unmated and those already mated among the ones kept for hunting — on smelling the male and hearing his call, some become full and some lay on the spot. The cause of this affection is the same as in humans and in quadrupeds: if their bodies happen to be in heat for intercourse, some emit semen at a mere sight, others at the slightest touch. Birds of this kind are by nature disposed to mate and are prolific in semen, so that they need only a slight stimulus when they happen to be in heat, and the discharge occurs quickly in them; the result is that in the unmated ones wind-eggs are formed, while in the mated ones the eggs grow and reach completion quickly. Of animals that lay their eggs outside the body, birds emit the egg complete, but fish emit it incomplete, and it takes its growth outside, as has also been said before.
10| The cause is that the fish kind is prolific in offspring; it is therefore impossible for it to bring many to completion, and that is why they lay them outside. And the emission is quick, for the wombs of fish that lay their eggs outside lie close to the vents. Now the eggs of birds are two-colored, but those of fish are all one-colored. The cause of the two-coloredness one may see from the capacity of each of the two parts, the white and the yolk. The secretion arises from the blood (for no bloodless animal lays eggs), and that blood is the matter for bodies has been said many times. Now one part of it is nearer to the form, as the parts come to be — the hot part; the other, more earthy part, provides the constitution of the body and is farther removed. This is why, in all eggs that are two-colored, the animal takes the starting point of its generation from the white (for the psychic principle is in the hot), and its nourishment from the yolk. In animals hotter by nature, then, that from which the starting point comes and that from which the creature is nourished are kept separate, and the one is white and the other yellow, and the white is always greater and purer in proportion than the yellow and earthy part;
11| but in animals less hot and moister, the yellow is greater and more fluid. This is what happens in marsh birds; for they are by nature moister and colder than birds that walk on land, so that the eggs of such birds have a great deal of what is called yolk, and it is less yellow because the white has been less fully separated out. And in creatures that are by now cold by nature among egg-layers, and moreover more moist still (such is the fish kind), the white is not even separated out at all, on account both of its smallness and of the abundance of the cold and earthy element; that is why the eggs of all fish are one-colored, being, as it were, white yolk, or yellow white. The eggs of birds, including wind-eggs, have this two-coloredness; for each has that from which each of the two parts will come — that from which the starting point comes and that from which the nourishment comes — but these are incomplete and still need the male; for wind-eggs become fertile if at some point they are mated by the male. The cause of the two-coloredness is not the male and the female, as though the white came from the male and the yellow from the female;
12| rather, both come from the female, but one is cold and the other hot. In those in which the hot is plentiful, it is separated out; in those in which it is little, it cannot be. That is why the conceptions of such creatures are one-colored, as has been said. The semen only brought it together. And for this reason the conception in birds appears at first white and small, but as it advances it becomes entirely yellow, as more and more blood-like matter keeps being mixed in; finally, as the hot is separated out, the white takes its place around it in a circle, as when a liquid boils, alike on every side; for the white is by nature fluid, but has within itself the psychic heat; this is why it is separated out in a circle, while the yellow and earthy part is within. And if one pours many eggs together into a bladder or something of the kind and boils them over a fire that does not make the motion of the heat faster than the separation that occurs within a single egg, then, just as in one egg, the resulting mass from all the eggs together has the yellow in the middle and the white in a circle around it.
13| Why, then, some eggs are one-colored and some two-colored has been stated. In eggs the principle of the male is separated out at the point where the egg is attached to the womb, and so the shape of two-colored eggs becomes unequal, not entirely round but sharper at one end, because it must differ at the point where it holds the white, in which it has its starting point. That is why the egg is harder there than below; for it must cover and guard the starting point. And for this reason the sharp end of the egg comes out last; for what is attached comes out last, and it is attached at the starting point, and the starting point is in the sharp end. The same manner holds also in the seeds of plants; for the starting point of the seed is attached in some cases within the branches, in others within the husks, in others within the fruit-coverings. This is clear in the case of legumes; for wherever the two-valved pod of beans and similar seeds is joined together, there the seed is attached, and the starting point of the seed is there. One might raise a difficulty about the growth of eggs, as to how it comes about from the womb. For animals take their nourishment through the umbilical cord, but through what do eggs take theirs?
14| since they do not, like grubs, get their growth through themselves. But if there is something by which the embryo is attached, where does this go when the embryo reaches completion? For it does not come out along with it, as the navel-cord does with animals born alive; rather, the surrounding shell forms once the embryo is complete. Now this question is rightly asked; but what escapes notice is that the shell which forms is at first a soft membrane, and only becomes hard and brittle once the embryo is complete, and in such due proportion that the chick comes out while it is still soft (for it would have caused pain in the hatching if it had not), and once it has come out it sets at once as it cools, since the moisture in it, being small in amount, quickly evaporates and the earthy part is left behind. Now a part of this membrane is at the outset navel-like at the pointed end, and while the embryo is still small it stands apart from it like a tube. This is clear in the case of small eggs that are cast out prematurely: if a hen, after being drenched or chilled in some other way, casts out an egg, the embryo still looks bloody and has running through it a small navel-like stalk. As the embryo becomes larger, this stalk is stretched tighter and becomes shorter. Once the pointed end of the egg is complete, this is the limit that results. Beneath this is the inner membrane, which separates the white from the yolk on the near side.
15| Once the egg is complete, the whole thing comes free, and reasonably enough the navel-cord no longer appears, for it is itself at the very tip. The manner of coming out is the opposite for animals from eggs as against those born alive: the latter come out head first, at the starting principle, while for the egg the coming-out is, so to speak, feet first. The cause of this is what has been said, namely that the attachment is at the starting principle. The generation from the egg comes about in birds through the hen's sitting on it and concocting it further, the animal being separated off from one part of the egg, while it takes its growth and reaches completion from the remaining part. For nature at the same time places in the egg both the matter of the animal and food sufficient for its growth; since the hen cannot bring it to completion within herself, she lays the food along with it in the egg. For animals born alive, the food is produced in a different part, the so-called milk, in the breasts; but for birds nature does this in the eggs, though in the opposite way from what people suppose and from what Alcmaeon of Croton says. For the white is not the milk, but the yolk;
16| for this is the food for the chicks, and people suppose it is the white because of the similarity of color. Now the chick comes about, as has been said, through the hen's sitting on the egg; but even so, if the season is temperate or the place where the eggs happen to lie is warm, the eggs of birds are concocted, and likewise those of four-footed egg-laying animals. For all such animals lay their eggs into the earth, and the eggs are concocted further by the heat in the earth. Those egg-laying and four-footed animals that go about sitting on their eggs do this more for the sake of protection. The eggs of birds and those of the four-footed animals come about in the same way: they too are hard-skinned and two-colored, and form near the membrane that divides them, just as those of birds do, and everything else, both inside and outside, comes about in the same way. So the same account holds for the cause in all these cases. But the eggs of the four-footed animals are concocted through their own strength and by the season, while those of birds are more perishable and need the mother that bore them. And nature seems to want to provide, in the case of offspring, a perceptive concern for their care; but in the worse animals it produces this only up to the point of giving birth, in others also through the completion of the young, and in those with more practical wisdom, through the rearing of the young as well.
17| In those that most share in practical wisdom there also comes about, toward the offspring once they are complete, familiarity and affection, as with human beings and with some of the four-footed animals, while for birds this lasts only up to the begetting and rearing of the young; and this is why females that do not sit on their eggs, once they have laid them, are worse off, as if deprived of something that belongs to them by nature. The animals in eggs reach completion more quickly on warm days, for the season works together with the process; concoction, after all, is itself a kind of heat. For the earth concocts further by its heat, and the sitting hen does this same thing, since she applies the heat within herself. And eggs also spoil and become what are called "wind eggs" more, reasonably enough, in the hot season; for just as wines turn sour in warm weather when the sediment is stirred up (this being the cause of the spoiling), so too in eggs it is the yolk that spoils, since this is the earthy part in both cases. This is why wine becomes turbid when the sediment is mixed in, and eggs that spoil do so through the yolk. Now with animals that lay many eggs, this sort of thing happens reasonably enough (for it is not easy to render the fitting heat to all of them alike, but it falls short in some and is excessive in others, and makes them turbid as if putrefying them), while for the hook-taloned birds, which lay few eggs, this happens no less;
18| for often one of a pair of eggs becomes a wind egg, and, one might almost say, a third of them always does; for being hot in nature, these birds make the moisture in the eggs as it were boil over. For the yolk and the white have, in fact, opposite natures. The yolk sets in frost, but becomes liquid when heated; this is why, when it is concocted further in the earth or by sitting, it becomes liquid, and being of this kind it becomes food for the animals forming in it. But when burned or roasted it does not become hard, because its nature is earthy in the way wax is; and for this reason, when heated further, if it is not formed of moist residue, it separates out and becomes a wind egg. The white, by contrast, does not set under frost, but rather becomes more liquid (the cause has been stated earlier), while when burned it becomes solid; this is why, as it is concocted in the course of the generation of the animal, it thickens. For the animal forms out of this, while the yolk becomes food, and the growth of the parts as they continually form comes from this source. This is why the yolk and the white are marked off separately by membranes, as having a different nature. As for the precise manner in which these stand to one another at the beginning of generation and as the animals are forming, and further concerning the membranes and navel-cords, one must look to what has been written in the Researches;
19| but for the present inquiry it is enough that this much be clear: once the heart has first formed, and the great vein has been marked off from it, two navel-cords stretch from the vein, one to the membrane surrounding the yolk, the other to the membrane shaped like a chorion, which surrounds the animal in a circle; this latter lies near the membrane of the shell. Through the one, then, the embryo takes its food from the yolk, and the yolk becomes more in quantity, for it becomes more liquid as it is heated. For the food, being bodily, must be liquid, just as it is for plants; and what forms first, both in eggs and in animals, lives the life of a plant at first, for it is by being attached to something that it takes its first growth and food. The other navel-cord stretches to the surrounding chorion. For one must suppose that egg-laying animals stand to the yolk in the way that the embryos of animals born alive stand to the mother, when they are in the mother (since egg-laying animals are of course not nourished within the mother, the yolk takes over a certain part of that role), while they stand to the outermost, blood-filled membrane as they stand to the womb.
20| At the same time, the shell of the egg has grown around both the yolk and the chorion (which is analogous to the uterus), as if someone were to place something around both the embryo itself and the mother as a whole. This is so because the embryo must be in the uterus and also with the mother. Now in live-bearing animals the uterus is in the mother, but in egg-laying animals it is the reverse, as if one were to say that the mother is in the uterus; for what comes from the mother, the nourishment, is the yolk. The cause is that the process of nourishing does not take place within the mother. As they grow, the umbilical cord leading to the chorion collapses first, because it is at this point that the animal must emerge, while the remainder of the yolk and the umbilical cord leading to the yolk come later. For what is generated must have nourishment right away: it is not suckled by the mother, and it cannot immediately provide itself with nourishment on its own. That is why the yolk, together with the umbilical cord, enters inside, and the flesh grows around it. So the animals generated from complete eggs outside the mother come about in this way, in birds and in those four-footed animals that lay the hard-shelled egg.
21| These things are more clearly visible in the larger animals; in the smaller ones they are unclear because of the smallness of their bulk. Further, the class of fishes is egg-laying. Of these, the ones that have the uterus below produce an incomplete egg, for the reason stated earlier, while those fish called the selachians produce a complete egg within themselves but bear live young outside, except for one, which they call the frogfish; this one alone lays a complete egg outside. The cause is the nature of its body: it has a head many times the size of the rest of its body, and this head is spiny and extremely rough. That is why it does not take its young back in afterward, nor does it bear live young from the start; for the size and roughness of the head prevents it from going in just as it prevents it from coming out. Now since the egg of the selachians is soft-shelled (for they cannot harden the covering around it, since they are colder than birds), the egg of the frogfish alone is solid and firm, for its safety outside, while the eggs of the others are by nature moist and soft, since they are sheltered inside by the body of the female that holds them. The generation from the egg is the same both for the frogfish, which complete their development outside, and for those that complete it inside; and this generation is in some respects similar to, and in others different from, that of birds.
22| For, first, they do not have the second umbilical cord that stretches to the chorion, which lies beneath the enclosing shell. The cause of this is that they do not have a surrounding shell. For it would be of no use to them: the mother provides shelter, whereas the shell is, for eggs laid outside, a protection against harm from without. Next, generation proceeds from the tip of the egg in these too, but not at the point where it is attached to the uterus; for birds develop from the pointed end, and that was the point of the egg's attachment. The cause is that the egg of birds separates from the uterus, whereas in these fish, not all of them but most, the complete egg remains attached to the uterus. As the animal develops at the tip, the egg is used up, just as in the case of birds and the other fish whose eggs have been released, and finally, once they are already complete, the umbilical cord is attached to the uterus. The same holds also for those whose eggs are released from the uterus; for in some of them, once the egg becomes complete, it is released. One might then raise the difficulty of why the modes of generation differ between birds and fish in this respect.
23| The cause is that the eggs of birds have the white and the yolk separated, whereas those of fish are of a single color, this substance being mixed throughout, so that nothing prevents the embryo from having its origin at the opposite point; for the substance is not of this uniform kind only at the point of attachment but also at the point directly opposite, and it is easier to draw nourishment from the uterus, by certain passages, from this opposite point of origin. This is clear in the case of eggs that are not released: in some of the selachians the egg is not released from the uterus but, remaining attached, moves down toward the place of live birth, and in these, once the animal is complete, it has its umbilical cord attached to the uterus, the egg having been used up. It is clear, then, that even earlier, while the egg still existed, the passages stretched from around it to the uterus. This occurs, as we said, in the smooth dogfish. So the generation of fish differs from that of birds in these respects, and for the reasons stated; but in other respects it occurs in the same way. For they too have the second umbilical cord in the same way: just as birds have theirs going to the yolk, so fish have theirs going to the whole egg (since it does not have a white part and a yolk part, but is entirely of one color), and they are nourished from this, and as it is used up the flesh likewise advances and grows around it.
24| Concerning, then, those fish that lay a complete egg within themselves but bear live young outside, generation occurs in this way, but most of the other fish lay their eggs outside, and all of them lay an incomplete egg except the frogfish; the cause concerning this one has been stated earlier. The cause has also been stated concerning those that produce incomplete eggs. The generation of these too from the egg occurs in the same way as that of the selachians that lay their eggs internally, except that their growth is rapid and starts from small beginnings, and the outer part of the egg is harder. The growth of the egg is similar to that of larvae: for animals that produce larvae also bring forth something small at first, and this grows through itself and not through any attachment. The cause is similar to what happens with leaven: for leaven too becomes large from a small amount, as its more solid part is moistened and its liquid part is turned into breath. In animals it is the nature of the vital heat that produces this, while in leaven it is the heat of the juice that has been mixed in. So the eggs grow of necessity for this reason (for they contain a leaven-like residue), but also for the sake of the better;
25| for it is impossible for them to receive their whole growth within the uterus, because of the great fecundity of these animals. For this reason they are secreted extremely small and undergo rapid growth: small, because the uterus is too cramped in relation to the multitude of eggs, and rapid, so that the offspring should not perish by lingering too long over their growth in the process of generation, since even as it is, many of the embryos that are produced perish; and that is why the class of fish is highly prolific. For nature counters the destruction by sheer numbers, and there are some fish that burst apart, such as the one called the garfish, because of the size of their eggs; for this fish, instead of having many embryos, has few large ones. For nature, taking away from their number, has added to their size.
26| We have said, then, that eggs of this sort grow, and for what cause. That these fish too lay eggs is shown by the fact that even the fish that bear live young, such as the cartilaginous fish, first lay eggs inside themselves. For it is clear that the whole class of fish is egg-laying, though none of these eggs reaches completion — in those kinds where there is a female and a male and the young are produced from mating — unless the male sprinkles his milt on them. There are some who say that all fish except the cartilaginous ones are female; they are not right. For they suppose that what are called their females differ from the males the way plants do, in cases where one bears fruit and the other is fruitless, for example the olive and the wild olive, the fig and the wild fig. And they suppose the same of fish, except the cartilaginous ones; about these they do not dispute. And yet the males are disposed in the same way as regards their milt-organs, both the cartilaginous kind and those belonging to the egg-laying class, and seed is seen being pressed out of both at the proper season. And the females also have wombs. But if the whole class really were female, then not only the egg-layers but the others too ought to have wombs — though wombs differing from those of the egg-layers, as mules do within the crested-tailed kind — with some of them simply barren.
27| As it is, some have milt-organs and others wombs, and in all cases except two, the red mullet and the channa, this is the difference: some have milt-organs, others wombs. The difficulty that leads people to suppose otherwise is easily resolved once one hears what actually happens. They say that none of the animals that mate produce many offspring, and in this they are right; for whatever generates complete animals or complete eggs from itself does not bear as many young as the egg-laying fish do, since the number of their eggs is immense. But they had failed to see this: that the case of fish eggs is not the same as that of birds' eggs. For birds, and such four-footed animals as lay eggs, and any of the cartilaginous fish that do so, produce a complete egg, which does not grow further once it has come out; but fish produce incomplete eggs, and the eggs get their growth outside, once laid. Further, the case is the same with the soft-bodied creatures and the crustaceans, which are actually seen mating, because their coupling lasts a long time; and among these it is evident that the one is male, and the other has a womb. And it would be absurd for this capacity not to exist throughout every class in the same way it does among the live-bearers, where one is male and the other female.
28| The cause of the ignorance of those who speak that way is that the differences bearing on the mating and generation of animals, being of every kind, are not obvious, and that, having observed only a few cases, they suppose things must hold the same way in all. That is also why those who say that female fish become pregnant by gulping down the seed speak this way without having grasped certain facts. For the males have their milt and the females their eggs at the same season, and the nearer the female is to laying, the more abundant and moister the milt becomes in the male. And just as the milt in the male and the egg in the female grow over the same period, so too their release happens together: the females do not lay all at once but little by little, nor do the males release their milt all at once. And all this happens for good reason. For just as the class of birds too, in some cases, produces eggs without mating — few, and rarely, though mostly from mating — this same thing happens with fish as well, though less often. And in both cases the spontaneous eggs are infertile unless the male sprinkles them, in whatever of these kinds there is also a male.
29| For birds, then, because their eggs come out complete, this must happen while they are still inside. But for fish, because their eggs are all incomplete and get their growth outside, even when the egg comes from mating, it is nonetheless preserved only by being sprinkled outside, and it is there that the males' milt gets used up. That is why it goes down and diminishes together with the eggs in the females, since the males always follow along, sprinkling the eggs as they are laid. It follows that all fish are male and female and all of them mate, except where in some class male and female are undifferentiated, and without the male's seed none of these creatures comes into being. What contributes to the error about them is also the fact that the coupling of such fish is quick, so that it escapes the notice of many even of the fishermen; for none of them observes anything of this kind for the sake of finding it out. But all the same, the coupling has been observed. For dolphins mate in the same way, coming alongside each other, as do those fish whose tail gets in the way. But in dolphins the separation takes longer, while in such fish it is quick. That is precisely why, not seeing this, but only the gulping-down of milt and of eggs, the fishermen too tell the naive and much-repeated story about the pregnancy of fish — the same one told by Herodotus the storyteller — that fish become pregnant by swallowing the milt, not realizing that this is impossible.
30| For the passage that goes in through the mouth leads to the stomach, not to the wombs; and whatever comes into the stomach must necessarily become food, since it is digested there, while the wombs are seen to be full of eggs — and where would these have entered from? The same holds also regarding the generation of birds. For there are some who say that crows and the ibis mate by the mouth, and that among four-footed animals the weasel gives birth through the mouth. These things are said by Anaxagoras and some of the other natural philosophers, who speak far too simply and without examination — in the case of birds, being deceived by an inference, because the mating of crows is seen rarely, while their touching bills together is seen often, something all crow-like birds do; this is clear in the case of tame jackdaws. The class of pigeons does the same thing, but because they are also seen mating, they have not acquired this reputation. The crow-like class is not much given to mating, since it is among the kinds that produce few young, though this too has in fact already been seen mating. And it is absurd not to reason out how the seed could reach the wombs, given that the stomach always digests whatever comes into it, just as it does food. These birds too have wombs, and eggs are seen near their diaphragms. And the weasel, like the other four-footed animals, has its womb in the same way they do —
31| from which, how could the embryo make its way to the mouth? Rather, it is because the weasel bears altogether tiny young, as do the other cloven-footed animals as well — about which we shall speak later — and because it often carries its young about in its mouth, that this belief has arisen. Also naive and quite mistaken are those who speak about the trochus and the hyena. For many say that the hyena, and Herodorus of Heraclea says that the trochus, has two genital organs, one male and one female, and that the trochus mates with itself, while the hyena mates and is mated in alternate years. But the hyena has been observed to have only one genital organ; for in some places there is no lack of opportunity to observe it. Rather, hyenas have, under the tail, a line resembling the female genital organ. Both the males and the females have this mark, but the males are caught more often; that is why, for those who observe it only in passing, this belief has arisen. But on these matters, enough has been said.
32| About the generation of fish, one might raise the difficulty: for what cause is it that among the cartilaginous fish neither are the females seen discharging their conceptions nor the males their seed, while among those that are not live-bearing, both the females discharge their eggs and the males their seed? The cause is that the cartilaginous kind is not prolific in seed at all. And further, the females among them have their wombs up near the diaphragm. For males differ from males and females from females in a similar way here: the cartilaginous fish are comparatively scant in what they produce toward generation. But the male kind among the egg-laying fish, just as the females discharge their eggs because of their quantity, so those males discharge their seed likewise. For they have more seed than is sufficient for mere copulation; nature prefers to spend the seed on helping the eggs grow further, once the female has laid them, rather than on the original formation alone. For as has been said both in the discussions above and just now, the eggs of birds are brought to completion inside the body, but those of fish outside it. For in a way the fish resemble the animals that produce grubs; for the grub-producing animals emit their conception in a still more incomplete state.
33| The male brings both kinds to completion — both the eggs of birds and those of fish — but for birds it does so inside (for their eggs are completed inside), while for fish it does so outside, because what is emitted is incomplete; since in fact the same thing turns out to hold in both cases. Now among birds, wind-eggs also become fertile, and eggs already covered by one kind of male change their nature toward the male that covers them afterward. And eggs of their own that are not yet grown, if the covering is interrupted, when covering happens again, are made to take on growth quickly — not, however, at every point in time, but only if the covering occurs before the change into the separating-out of the white. But for fish nothing of this sort is fixed; rather, for the sake of preservation the males discharge their seed quickly. The cause is that this is not on account of coloring; and that is why no such fixed season is set for these as for birds. And this comes about reasonably: for when the white has been marked off from the yolk, and the two are separated from each other, the egg already has the principle that comes from the male; for it is into this that the male contributes. The wind-eggs, then, take on generation only up to the point that is possible for them.
34| For it is impossible for them to be brought to completion as an animal (since that requires perception), yet the nutritive power of the soul belongs to females and males and all living things alike, as has often been said; and this is why such an egg, considered as a conception of a plant, is complete, but considered as that of an animal, incomplete. If, then, there were no male present in their kind, it would come about as it does among fish, supposing there really is such a kind as generates without a male; and it has been said about them before that this has not yet been adequately observed. As things stand, however, in all birds there is a female and a male, so that in the respect in which it is like a plant, the egg has reached completion (which is why it does not change again after covering), while in the respect in which it is not like a plant, it has not reached completion, and nothing else comes out of it; for it has come to be neither simply as the conception of a plant nor, from pairing, as that of an animal. Eggs that arise from covering, and that have separated out into a white, come to be according to whichever male covered first; for they already possess both principles.
35| In the same way the soft-bodied animals also produce their offspring — for instance cuttlefish and the like — and the crustaceans, for instance crayfish and their kin; for these too give birth from covering, and the male has often been observed pairing with the female. Hence those who say that all fish are female and give birth not from covering are shown not even to be reporting accurately in this respect either. For to suppose that these creatures give birth from covering, but those others do not, is strange; and if this had escaped notice, it would be a sign of inexperience. The pairing of these animals lasts longer than that of any others, as with insects — reasonably so, since they are bloodless, and therefore cold in nature. Now in cuttlefish and squid the eggs appear as two, because the womb is jointed and appears cleft in two, whereas in octopuses the egg is one. The cause is that its shape is round in form and spherical; for the division is not apparent once it is filled out. The womb of crayfish is likewise cleft in two. These animals too all expel their conception incomplete, for the same cause. Now the crayfish-like animals produce their offspring by themselves, apart from the male (which is why their females have larger tail-flaps than the males, for the sake of guarding the eggs), while the soft-bodied animals produce theirs outside the body.
36| And on the females of the soft-bodied animals the male sprinkles his seed, just as male fish do on the eggs, and it becomes continuous and sticky; but among the crayfish-like animals nothing of this sort has been observed, nor is it reasonable to expect it. For the conception is under the female and is hard-shelled, and it takes its growth, both in these and in the soft-bodied animals, outside the body, just as in fish also; and the cuttlefish that is coming to be grows attached to the eggs at the front part, for only there is this possible, since only there does it have its hind part and its front part meeting at the same place. As for the shape of the position it holds while coming to be, one must examine this from the observed records.
37| Concerning the generation of the other animals, then — land animals, winged animals, and swimming animals — an account has been given. About insects and the shelled animals we must speak according to the method laid down. Let us speak first about insects. That some of these arise from covering and others spontaneously has been said before, and in addition, that they produce grubs, and for what cause they produce grubs. For pretty much all animals seem in some way to produce a grub first; for the most incomplete kind of conception is of this sort. In all animals, both the live-bearing and the egg-laying, the complete egg is a conception that, being at first undifferentiated, takes on growth; and such is the nature of the grub. After this stage, some lay a complete egg, others an incomplete one that becomes complete outside, just as has often been said in the case of fish. Those that bear live young within themselves become, in a way, after the initial formation, egg-shaped; for the fluid is enclosed by a thin membrane, just as it would be if one stripped the shell off an egg — which is why they call the destructions of conceptions that occur at that stage 'discharges.' Insects both produce offspring that produce grubs, and those offspring that come to be not through covering but spontaneously arise first from a formation of this same kind.
38| For one must count caterpillars too as a species of grub, and likewise the offspring of spiders. And yet, because of the roundness of their shape, some of these and many other creatures might seem to resemble eggs; but one should not judge by shape, nor by softness and hardness (for the conceptions of some of these do become hard), but by whether the whole changes, and the animal does not come to be out of some one part. All the grub-like creatures, once they have advanced and reached the limit of their size, become like an egg; for the covering around them hardens, and at that time they become motionless. This is clear in the grubs of bees and wasps, and in caterpillars. The cause of this is that nature, as it were, lays her eggs before their time because of her own incompleteness, the grub being, as it were, still a soft egg in the process of growth. And the same thing happens in the same way in all the other cases of creatures not arising from covering, in wool or in certain other such materials, and in those that arise in water. For all of them, after the nature of the grub has become motionless, and the covering has dried all around, then, once this has broken open, the animal comes out as if out of an egg, brought to completion at this third stage of generation — of which most are winged, among the land animals.
39| What has justly been marveled at by many also turns out to fit the pattern we have described. For caterpillars, once they have taken food at first, later on take none, but become motionless — the things some people call chrysalises — and so do the grubs of wasps and bees. After this the things called nymphs come to be, and these no longer have anything of that sort; for the nature of eggs too, once it reaches its completion, no longer grows, though at first it grows and takes nourishment, until it is marked off and becomes a complete egg. Of the grubs, some have within themselves that from which, as they are nourished, such a residue comes to be added on, as with those of bees and wasps; others take it from outside, as do caterpillars and some of the other grubs. Why, then, such things come to be threefold in kind, and for what cause, having been in motion, they become motionless again, has been stated. Some of them come to be from mating, as with birds and the live-bearing animals and most fish, others spontaneously, as with some of the things that grow.
40| The generation of bees involves a great deal of difficulty. For since there is also, among fish, a certain kind of generation in some of them such that they produce offspring without mating, this appears, from what is observed, to hold also for bees. For necessarily either they bring the brood from elsewhere, as some say — and this either growing up spontaneously or being born of some other animal — or they beget it themselves, or they bring one kind and beget another (for this too some say, namely that they bring only the brood of drones); and if they beget, either while mating or without mating; and if while mating, either each kind begets its own kind by itself, or one of them begets the others, or one kind pairs with a different kind — I mean, for example, that bees come to be from bees pairing, drones from drones, and the kings from the kings, or that all the others come from one kind, namely from the ones called kings and leaders, or from the drones and the bees; for some say that some of these are male and others female, for instance that the bees are male and the drones female. But all these views are impossible for anyone reasoning it out, some on the basis of facts peculiar to bees, others on the basis of facts more common to the other animals.
41| For if, without giving birth themselves, they bring the brood from elsewhere, then bees ought to come to be even without bees bringing it, from the very place from which they bring the seed. For why should there be generation once it has been carried away, but not there in the place itself? For it makes no difference whether it grows spontaneously among the flowers or is born of some animal. And indeed if the seed belonged to some other animal, that animal ought to come to be from it, and not bees. Further, it is reasonable that they should carry off honey (for that is food), but that they should carry off brood belonging to another and not being food is absurd. For what purpose would they do it? For all creatures that busy themselves about their young labor over the brood that appears to be their own. But moreover it is not reasonable either that the bees should be female and the drones male; for nature gives the weapon for fighting to none of the females, yet drones are stingless while all bees have a sting. Nor is the opposite reasonable, that the bees are male and the drones female; for it is not the habit of any of the males to labor over the young, yet as things are the bees do this. And in general, since it is evident that the brood of drones comes to be even when there is no drone present, while that of bees does not come to be without the kings — which is why some say that only the drones' brood is carried in from outside — it is clear that they are generated neither from mating, nor from each kind pairing with its own kind, nor from bees and drones together.
42| That they carry in only this brood is impossible for the reasons stated, and it is not reasonable that a like state of affairs should not hold for their whole kind. But moreover it is not possible either that the bees themselves should be some male and some female; for in all kinds the female differs from the male. And in that case they would be begetting themselves; but as it is, their brood evidently does not come to be unless the leaders are present, as they say. And common to both the theory of generation from one another and that from the drones — whether apart or together — is the fact that none of them has ever been observed mating; whereas if there were among them a female element and a male element, this would often have been observed happening. It remains, then, if generation is by mating, that the kings beget by pairing. But drones are evidently generated even when no leaders are present, and it is not possible either for the bees to bring in their brood or for them to beget them by mating. It remains, then — just as appears to happen in the case of certain fish — that the bees beget the drones without mating, being female with respect to begetting, but having within themselves, as plants do, both the female and the male.
43| That is also why they have the organ for fighting; for one ought not call a thing female in which the male is not separated out. And if this evidently holds true of the drones, that they too come to be not from mating, then the same account must necessarily hold also for the bees and the kings, and they too are not generated from mating. If, then, the brood of bees had evidently come to be present without the kings, it would have been necessary that the bees also come to be from themselves without mating. But as it is, since those who occupy themselves with the keeping of these animals say this does not happen, it remains that the kings both beget themselves and beget the bees as well. And since the kind of bees is remarkable and peculiar, their generation too evidently proves to be peculiar. For that bees should beget without mating might occur among other animals as well, but that a kind should beget a different kind is peculiar to them; for red mullets beget red mullets and sea-perch beget sea-perch. The reason is that the bees themselves are begotten not as flies and such animals are, but from a different kind, though one akin to them. For they come to be from the leaders.
44| For this reason their generation stands, in a way, in due proportion. For the leaders are like the drones in size, but like the bees in having a sting. The bees, then, resemble them in this respect, the drones in size. For there must necessarily be some point of divergence, if the same kind is not always to come to be from each; and this is impossible, for then the whole kind would consist of leaders. The bees, then, are made like them in power and in the capacity to give birth, the drones in size; and if the drones also had a sting, they would be leaders. As it is, this remains the residue of the difficulty: the leaders resemble both kinds in the same respect, having a sting like the bees and being of the size of the drones. And it is necessary that the leaders too come to be from something. Since, then, they come neither from the bees nor from the drones, it is necessary that they beget themselves as well. Their cells come to be at the end, and are not many in number. So it turns out that the leaders both beget themselves and beget another kind besides (and this is the kind of bees), while the bees beget another kind, the drones, but no longer beget themselves — this having been taken away from them.
45| Since what is in accordance with nature always has order, it is necessary that the drones too should have been deprived of the power to generate any further kind. And this is in fact what is observed to happen: the drones themselves come to be, but generate nothing else, and generation comes to an end at this third stage in the series. And nature has put things together so well in this respect that the kinds always continue in being and nothing is lacking, even though not all of them generate. It is also reasonable that this should happen: in favorable seasons much honey and many drones are produced, while in rainy seasons offspring in general are abundant. For excessive moisture produces a greater residue in the bodies of the leaders, while favorable seasons do so in the bodies of the ordinary bees; for since the bee is smaller in size, it stands more in need of a favorable season. And it is well arranged, too, that the kings, as though made for the purpose of breeding, remain within, released from the necessary tasks, and that they have size, as though their bodies were constituted with a view to procreation; and that the drones are idle, since they have no weapon with which to fight for food, and because of the slowness of their bodies. The bees are intermediate in size between the two (for in this way they are useful for the work), and are workers, in that they feed both the young and the fathers.
46| It is also agreed that the fact that the generation of the bees follows from the kings is confirmed by what accompanies it: for if there were nothing of this sort, the facts about their sovereignty would make no sense; and so is the fact that the kings are left doing no work, as being parents, while the drones are punished as children — for it is more fitting to punish children, and those who have no function. And the fact that the bees, though few in number themselves, that is the leaders, generate the bees in great numbers, seems to be something like what happens in the generation of lions, which at first produce five cubs, later fewer, and finally one, and then none. The leaders similarly produce a multitude at first, but later few, themselves being few, and their offspring less than that of the lions; but since nature took away from their numbers, it gave them size in return. From argument, then, the facts about the generation of bees appear to be of this character, and also from what is thought to happen concerning them; the facts, however, have not yet been adequately grasped, but whenever they are grasped, then perception is to be trusted more than arguments, and arguments too, provided they are shown to agree with what appears. A sign against their coming to be from mating is also the fact that the brood appears small in the cells of the comb —
47| whereas all the insects that are generated from mating pair for a long time, but give birth quickly, to something worm-shaped in size. Concerning the generation of the kinds related to bees, such as hornets and wasps, it happens in a manner similar in a way to all of them, but the extraordinary element has reasonably been taken away, since they possess nothing divine, as the kind of the bees does. For the ones called mothers generate, and they mold the first parts of the combs, and they generate by mating with one another; for their pairing has often been observed. But how many differences each of these kinds has, either from one another or from the bees, must be studied from what has been recorded in the Researches on Animals.
48| We have now spoken of the generation of all the insects; we must next speak of the testaceans. The facts about their generation are in one respect similar to those of the other animals, in another respect not, and this happens reasonably. For in relation to animals they resemble plants, and in relation to plants they resemble animals, so that in one way they appear to come to be from seed, in another way not from seed, and in one respect spontaneously, in another from themselves — or rather, some in the one way, some in the other. And because their nature stands in an inverse relation to that of plants, for this reason on land either no kind of testacean comes to be, or only a small one, such as that of the snails, and if there is some other such kind, it is rare; whereas in the sea and similar liquids many come to be, and of every sort of shape. The kind of plants, on the other hand, is small in the sea and such liquids, and practically nonexistent, while on land all such things come to be. For nature holds an analogous relation and is divided proportionally: by as much as the moist is more life-giving than the dry, and water than earth, by that much does the nature of the testaceans exceed that of the plants, since it is nature's intent that as plants are to earth, so testaceans should be to the moist, so that plants are, as it were, land-oysters, and oysters are, as it were, water-plants.
49| And for a cause of this sort, the things in the moist are also more varied in form than those on land. For the moist has a nature more easily molded than that of earth, and is bodily not much less so, and this is especially true of the things in the sea. For fresh water is sweet and nourishing, but less bodily and cold. Hence all the bloodless creatures whose nature is not hot do not come to be in lakes, nor among salt waters in the fresher parts, but less so — for example the testaceans, the mollusks, and the crustaceans (for all these are bloodless and cold in nature) — but they come to be in lagoons and near the mouths of rivers. For they seek warmth and nourishment at the same time, and the sea is far more moist and bodily than fresh water, and hot in nature, and shares in all the parts — moisture, breath, and earth — so that it also shares in all the animals that come to be severally in each of these regions. For one might suppose the plants belong to earth, the aquatic creatures to water, and the land animals to air; and the more and less, the nearer and farther, produce a great and remarkable difference.
50| The fourth kind is not to be sought in these regions; and yet it wants, in a way, to hold a rank corresponding to that of fire, for fire is counted as the fourth of the bodies. But fire always appears not to have its own proper form, but to exist in one of the other bodies; for what has been set on fire always appears to be air, or smoke, or earth. But such a kind must be sought in the region of the moon; for the moon appears to share in the fourth remove. But concerning these matters there would be another discussion. The nature of the testaceans is constituted, in some cases spontaneously, in others by certain creatures emitting some power from themselves, and often these too come to be from a spontaneous formation. We must next take up the generation of plants. Of these, some come to be from seed, others from cuttings that are planted out, others by putting out side-growths, as the kind of onions does. It is in this way, then, that the muscle-shells come to be; for smaller ones are always growing on beside the original one. But whelks, purple-fish, and those said to form combs emit, as it were from a seminal nature, mucous fluids. None of these should be thought to have seed, but rather, in the manner described, to share in a likeness to plants.
51| That is also why a multitude of such creatures arises, once one has come to be even a single time. For all of these do in fact happen to arise spontaneously, but it is more in accordance with reason that they should also form once something already exists. For it stands to reason that some residue is produced in addition at each starting-point, from which each of the things that grow alongside it puts out its shoot. And since nourishment and the residue of nourishment have a similar power, it is likely that the substance of the things that form comb-like is similar to the original composition from which it arose. That is why it is reasonable that generation should also occur from this residue. But whatever neither puts out a shoot nor forms comb-like, the generation of all of these is spontaneous. All the things that form in this way appear both in earth and in water, coming to be through a kind of putrefaction, with rainwater mingled in. For when the sweet element is separated off into the forming starting-point, the residue that is left over takes on such a shape. Nothing comes to be by putrefying but by being concocted; putrefaction, and the putrefied residue, belong to what has been concocted. For nothing comes from just anything, any more than in the things fashioned by craft — for then there would be no need to make anything at all; but as it is, craft removes what is useless from the material, and so does nature. Animals and plants come to be in earth and in moisture because water is present in earth, and breath is present in water, and in all of this there is soul-heat, so that in a way everything is full of soul.
52| That is why it forms quickly, whenever it is enclosed all around. And it is enclosed and comes to be, as the bodily fluids are heated, like a frothy bubble. Now the differences by which one kind is more honorable and another less honorable in what forms lie in the enclosure of the soul-starting-point. Responsible for this too are the places, and the body that does the enclosing. In the sea there is much of the earthy element present; that is why the nature of the shellfish forms out of just such a composition: the earthy part hardens all around and sets with the same setting as bones and horns (for these cannot be melted by fire), while inside is enclosed the body that has life. But whether the generation of these creatures comes only from pairing or not has not yet been adequately worked out. Someone wishing to inquire correctly would ask what it is that forms according to the material starting-point in such cases. For in females, this is a certain residue of the animal, which the moving starting-point from the male — being potentially such as that from which it came — brings to completion as the animal. But in this case, what should one call such a thing, and where does it come from, and what is the moving starting-point corresponding to the male?
53| We must grasp that even in the animals that reproduce in the ordinary way, the heat within the animal, by separating off and jointly concocting the nourishment that enters it, produces the residue that is the starting-point of the embryo. It is the same in plants too, except that in plants, and in some animals, there is no need at all for the starting-point from the male (for they have it mixed in within themselves), whereas the residue of most animals does need it. Nourishment is for some water and earth, for others what comes from these; so that what the heat in animals produces out of nourishment, the heat of the season in the surrounding air produces likewise, drawing together matter from sea and earth by concocting it and forming it into a composition. And what is caught and enclosed, or separated off, within the breath belonging to the soul-starting-point produces an embryo and puts motion into it. Now the composition of the plants that come to be spontaneously is uniform in kind, for each comes from some one part, and one portion becomes the starting-point while the other becomes the first nourishment for the things that sprout. But among animals, worm-birth occurs both among the bloodless creatures that do not come from other animals, and among the blooded ones — for example a certain kind of grey mullet and other river fish, and further the kind of eels.
54| For all of these, although their nature has little blood, are nonetheless blooded, and they have a heart, the blood-related starting-point of their parts. What are called earth's-guts have the nature of a worm, and it is within these that the body of eels comes to be. That is also why, concerning the generation of human beings and four-footed animals, one might suppose — if indeed they were once earth-born, as some say — that this happens in one of two ways: either the first thing forms as a worm forms, or it comes from eggs. For it is necessary either that they have the nourishment for growth within themselves (and an embryo of that kind is a worm), or that they receive it from elsewhere, and this either from the thing that bore them or from a part of the embryo itself. So if the one is impossible — flowing in from the earth the way it flows in from the mother in the other animals — it is necessary that it be received from a part of the embryo; and we call generation of this kind generation from an egg. That, then, if there was indeed some starting-point of generation common to all animals, it is reasonable that it be one of these two is clear; but generation from eggs has the lesser claim to reason. For we see no animal generated in that way, but rather in the other way, both among the blooded creatures just mentioned and among the bloodless ones.
55| Such are some of the insects, and the shellfish, which are our subject here; for they do not come to be from any one part, as egg-born creatures do. And they carry out their growth in the same way as worms do. For worms grow upward from the start, since the nourishment for the upper part lies in the lower part. And this holds in the same way for creatures from eggs too, except that in those the whole is used up, whereas among the worm-born creatures, once the upper part has grown from the composition in the lower part, the lower part is then in turn articulated out of what remains. The reason is that in all of them, afterward, the nourishment comes to be in the part beneath the diaphragm. That the worm-like creatures carry out their growth in this way is clear in the case of bees and the like: at the start they have the lower part large and the upper part smaller. And in the shellfish too, the process of growth works the same way. This is also evident in spiral-shelled creatures, in their coils: for as they keep growing, more coils form toward the front and toward what is called the head. The manner, then, in which generation occurs both for these and for the other spontaneously-generated creatures has, roughly speaking, now been stated.
56| That all shellfish form spontaneously is clear from facts of the following kind: they form near ships when the frothy slime putrefies, and in many places where previously nothing of the sort existed, later, because the place lacked moisture and turned to mud, the so-called lagoon-oysters among the shelled creatures came to be — for example near Rhodes, when a naval fleet put in and earthenware jars were thrown into the sea, and after time had passed and mud had gathered around them, oysters were found inside. And here is proof that such creatures release nothing generative from themselves: when some Chians transported live oysters from Pyrrha in Lesbos and released them into certain strait-like places of the sea resembling their original habitat, no greater number of them came to be over time, though their size increased considerably in growth. What are called their eggs contribute nothing to their generation, but are a sign of good nourishment, like fatness in blooded creatures; that is also why they become good-flavored for eating at these seasons. A sign of this is that some always have them, such as the pinna, the whelk, and the purple-shell, except that at one time they are larger, at another smaller. Others do not always have them, but have them in spring, and as the season advances they diminish, and in the end disappear altogether — for example scallops, mussels, and the so-called lagoon-oysters.